The three long bones of the upper extremity are the humerus, radius and ulna. The distal portion of the humerus and the proximal portions of the radius and the ulna form the elbow joint. Elbow fractures account for only about 5-8% of all fractures and occur most commonly in older people as a result of a fall. The functional outcomes of elbow fractures often include high rates of joint stiffness, loss of range of motion and non-union.
Orthopedic surgeons generally follow certain principles for the proper internal fixation of the bones of the elbow joint. Each screw used to attach the plate to the bone should be as long as possible and engage as many articular fragments as possible. The screws should lock to the plate and interdigitate to create a “fixed angle” structure. The plate must be strong and stiff enough to not break or bend under load. Adhering to these principles for elbow fracture repair is particularly challenging given the difficulty of the surgical procedure and the anatomical variation among patients.
In addition, a bone plate attached to the surface of a fractured bone of the elbow joint may tend to stand “proud” of the bone surface. Currently available plates do not fit well on the bone surfaces without impinging on soft tissue or obstructing the natural articulation of the joint. One bone plate shape, even if provided for each type of elbow fracture and in different sizes, cannot accommodate all the anatomical differences among patients.
About half of all elbow fractures are radial head fractures and about a fifth involve fracture of the radial neck or proximal radius. Because of the considerations just stated, surgeons generally prefer not to use bone plates to treat the fractured proximal radius. Depending on the extent of comminution of proximal radius fractures, surgeons may instead use external fixation or screws and pins together with post operative therapy.
Fractures of the coronoid, which is located on the proximal ulna, are typically small but difficult to treat. Proper treatment is important since the coronoid fracture may have a heavy impact on overall elbow stability. Traditional fixation of these fractures involve capture of the coronoid fragments with screws or sutures coming from the posterior side of the ulna. This type of fixation may not be stable enough to resist the strong anterior dislocating force of the distal humerus.
The olecranon is located on the posterior side of the proximal end of the ulna and articulates in the olecranon fossa. The olecranon is not covered with thick layers of soft tissue and is particularly vulnerable to external impacts and fracture. The olecranon also is the attachment location of the triceps muscle used in extension of the arm, and transfers very high forces.
In addition to fractures of the olecranon, the surgeon may intentionally sever the olecranon from the proximal ulna during an osteotomy procedure in order to reflect the triceps muscle, thereby obtaining improved surgical access to the distal humerus. Once the repair to the humerus has been completed, the surgeon then may use a bone plate to reattach the olecranon to the proximal ulna.
Currently available fracture fixation plates for the medial, lateral and posterolateral parts of the distal humerus do not consistently match the contour of the bone surface. Due to the anatomical differences between patients, a single bone plate configuration, as initially provided to the surgeon, is unlikely to conform perfectly to the bone surface, even if that plate was specifically designed for that particular type of bone. Therefore, some manufacturers provide numerous sizes and configurations of bone plates for a particular portion of a specific bone. Since selecting the right plate involves subjectivity, clinical outcomes may not be highly consistent.